> 
> | Also, you say a dependency with zero variables on the right side is
> | syntactically correct, but later you say it will be reported as an
> | error because it says nothing.  Why bother?
> 
> Point taken.  In fact that same database text I mentioned above
> prohibits functional dependencies in which either side is empty.
> But it turns out that the two extremes ("a ->" and "-> a") are
> rather interesting so I didn't want to exclude either as being
> syntactically well-formed.  Rejecting the former at a later stage
> was a design decision, intended only to catch errors, and isn't
> an essential part of the design.
> 
> All the best,
> Mark

Should redundant dependencies trigger an error or a warning? I'd say that if
I'm writing some haskell code, I wouldn't mind if a redundancy is flagged as
an error; most likely, it'd take a short time to fix. However, if someone is
generating haskell automatically (maybe with Derive, PolyP, a GUI designer,
...), the easiest thing to do is to generate all the dependencies that will
make the types correct, without trying to avoid redundancies. In this case,
I think a warning is better. 

Just my 2 cents. 

Fermin




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